"use every month" is obvious and total bullshit, completely ridiculous.
The problem is, you are not going to get very good and exact data from the manufacturers on this. It will be mostly anecdotal which I think you'll hate to hear.
Capacitor manufacturers leave this thing for the product designers to figure out, and the product designers then tend to ignore the problem and leave it to the end users unhandled.
Personally, I think the problem is way exaggerated by some. I have seen many elcaps die when overstressed by excessive ripple currents in hot environment, i.e. die in usage, but I have never seen an elcap die after powering up after long storage period. (I don't say it doesn't happen, just I have never seen it.)
Agreed. Manufacturers will give an 'specified' shelf life figure for new parts in storage under specified ambient conditions prior to equipment manufacture, but use cases are far too diverse for them to give a sensible and repeatable figure beyond that.
I, like many others, have some really old capacitors in test equipment which hardly ever get powered up. I take the approach of powering them up occasionally on a 'when I remember' basis, not specifically for the electrolytics but for the equipment in general - I think it generally does them good. Warming them up keeps moisture out of PCBs, transformers, exercises fan bearings, help Tantalum bead capacitors last longer etc. I've never had a power supply electrolytic capacitor fail after storage either.
Again, like many others, I have electrolytics hidden away in drawers that are 40+ years old, I might occasionally pull one out to use for something but have never seen any problems if they show no physical signs of deterioration. It seems a shame to bin them.
There might be some cases where higher initial electrical leakage might be a problem, for instance a coupling cap in a signal path, where it might temporarily interfere with biasing, but the circuit should be designed to cope with the leakage of a brand new capacitor at the limit of its shelf life anyway, I would count that as a design weakness anyway. That would be an exceptional case though, a bit of initial additional leakage in a cold capacitor wouldn't typically be noticeable.